It is well-known to use pyrazolotriazole couplers for forming magenta dyes in photographic elements. One type of coupler used for this purpose is a 1-H-pyrazolo(5,1-c)-1,2,4-triazole coupler. An example of such a coupler is shown in Romanet et al. U.S. Pat. No. 5,183,728. The couplers shown in the Romanet patent contain a nitrogen in a position beta to the carbon in the 3-position of the pyrazolotriazole nucleus. The preferred coupler of the Romanet patent is shown as Compound V at column 25 of the patent. This compound corresponds to comparative coupler C-1 in the present application.
The couplers of the Romanet patent were found to exhibit a desired level of reactivity and to produce a dye having a very satisfactory hue. However, the coupler of Romanet has been found to have an undesirable sensitivity to the pH of the developer solution used when processing a photographic element containing the coupler to develop an image. The result is that the relationship between the amount of exposure and the resulting dye density (the D-LogE curve or gamma) varies for the coupler as a function of the pH of the processing solution.
It is, of course, essential that a photographic element having a particular latent image produce the same resulting viewable image upon development regardless of the minor variations in the maintenance of the target pH values in the developer solution that are typical in the processing business.
Moreover, the couplers of Romanet should contain water-solubilizing groups in order to have high reactivity towards oxidized developer. This results in high imaging efficiency. However, these same substituents also cause the couplers to partially or totally dissolve at the high pH of the developer solution and diffuse (wander) into other imaging layers where it can react with the oxidized developer generated in that layer. This leads to undesirable color contamination. Reducing the degree of water solubility of the coupler can minimize coupler wandering but also decreases the ability of the coupler to react with oxidized developer.
Additionally, it is desirable to generate a photograpic element that has minimal dye density in the regions of no or very low light exposure. When silver develops in this exposure region, the resulting unwanted dye density adds noise to the system, lowers contrast, adds to variability in the process and increases printing time resulting in decreased photofinisher output. It is important that a coupler exhibit high reactivity toward oxidized developer without forming too much dye with the silver developed in the low exposure regions.
Thus, it is a problem to be solved to provide a photographic element that contains a magenta dye-forming coupler which is much less sensitive to variations in the pH value of the developer solution than is the case with elements containing couplers previously known while maintaining high imaging efficiency and without color contamination due to coupler wandering or high fog readout as measured by green Dmin.